Store-operated cation entry mediated by CD20 in membrane rafts

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• B cell activation depends on sustained calcium influx via store-operated calcium (SOC) channels.
• The precise molecular identity of SOC channels remains elusive.
• CD20, a raft-associated tetraspan protein, is implicated in B cell function.

Purpose of the Study:

• To investigate the molecular identity of SOC channels involved in B cell activation.
• To determine the role of CD20 in store-operated calcium entry.
• To characterize the functional properties of CD20-associated SOC channels.

Main Methods:

• Ectopic expression of CD20 in Chinese hamster ovary (CHO) cells.
• Assessment of calcium and strontium influx through SOC pathways.
• Functional analysis of CD20 mutants lacking raft-localization sequences.
• Downregulation of CD20 expression using short interfering RNA (siRNA).
• Cholesterol depletion experiments.

Main Results:

• Ectopic CD20 expression in CHO cells created a novel SOC entry pathway permeable to both calcium and strontium.
• Deletion of a cytoplasmic sequence in CD20 abolished SOC pathway activity, correlating with impaired raft localization.
• Strontium-permeable SOC channels were identified in B cells.
• B cell receptor-stimulated calcium influx was significantly reduced by CD20 downregulation and cholesterol depletion.

Conclusions:

• Raft-associated CD20 is a component of the store-operated calcium (SOC) entry pathway activated by the B cell receptor.
• CD20 plays a critical role in regulating calcium influx necessary for B cell activation.
• This finding provides the first evidence for CD20's direct involvement in SOC channel function.